Receiving circuit



'April 5, 1938. E. EBBIGHAUSEN RECEIVING CIRCUIT Filed Jan. 9, 1936 A w A v A HL-In-u INVENTORY E. EBBIGHAUSEN BY Hg ,g/LJVW ATTORNEY Patented Apr. 5, 1938 UNITED STATES PATENT OFFICE RECEIVING CIRCUIT tion of Germany Application January 9, 1936, Serial No. 58,299 In Germany January 16, 1935 Ciaims.

This invention relates to a radio receiving circuit and more particularly to means for controlling the selectivity and tonal qualities thereof. A feature of the invention consists in the use 5 of a diode detector feeding into an audio amplifier tube, the high frequency transmitted to the first audio-frequency tube being back coupled to the diode circuit by means of inductive coupling, and variable means controlling in inverse sense the width of the frequency bands transmitted through the radio frequency and audio frequency portions of the receiver.

The invention is embodied in the single figure of the drawing forming part of this application.

Referring now to the figure, an antenna coil for supplying the high-frequency is designated by I.

Coupled thereto is the tunable circuit 2 and 3 which is connected between anode and cathode of the diode detector 4. Resistance 5 is connected between the cathode and the tunable circuit and constitutes the detector output or load impedance.

The high potential side of this resistance is connected to the control grid of the next tube 1.

There appears at resistor 5 on the one hand, the

alternating audio-frequency voltage, and if feed back is not desired, a condenser of suitable capacity may be provided across the resistor for bypassing the rest of the high-frequency.

For the purpose of obtaining a feed back action and a control thereof, the following measure is proposed in accordance with the invention.

A variable condenser 6 is chosen by means of which the high-frequency current across condenser 8 and coupling coil 9, will be controlled.

35 Hence, the feed back occurs across tube 1, condenser 8, and coupling coil 9; it being necessary, in this case, that high-frequency reaches the grid of tube 7, the capacity of the condenser 6 should therefore not exceed a certain value.

40 The circuit offers the following advantages: If

the damping of the apparatus is very highly reduced on account of the feed back, the selectivity increases and the cutting of the side band becomes further extended, i. e., the tones of high pitch will 45 be suppressed. In this case, the capacity of condenser 6 is small, i. e., the tones of high pitch are cut as little as possible at the grid of the audiofrequency tube. If there is a smaller damping reduction of the apparatus, the cutting of the side band in the tunable circuit 2 and 3 is less extensive. But at tube 1, a somewhat greater cutting of the high pitch tones is to be taken into account, so that the timbre of the apparatus is uniform at various feed back factors.

What I claim is:

1. A circuit arrangement comprising a detector, a radio frequency tunable circuit constituting the input to said detector, an audio frequency amplifier, and means for coupling said amplifier to the output of said detector, said coupling means including a single variable element for controlling the width of the frequency bands transmitted through the radio frequency and audio frequency portions of the circuit and for simultaneously controlling in inverse sense the transmission of high audio frequencies through the audio frequency amplifier.

2. A circuit arrangement comprising a diode rectifier provided with a tunable input circuit and a load circuit having appreciable impedance to both radio frequency and audio frequency, an audio amplifier coupled to said load circuit and having means for feeding radio frequency from the amplifier output back to the resonant circuit, and means for simultaneously and substantially varying the impedance of said load circuit for both radio frequency and audio frequency.

3. Coupling means for conveying energy from a resonant circuit to an amplifier including a diode and a load circuit energized by said resonant circuit, means for feeding radio frequency from the amplifier output back to the resonant circuit, and connections for energizing said amplifier input from the voltage drop across said load circuit, said load circuit having sufficient impedance at both the resonant circuit frequency and at audio frequency to provide substantial voltage at radio frequency to said amplifier.

4. The invention defined in claim 3 including means for varying the load impedance for controlling both audio frequency and radio frequency transmission.

5. The invention defined in claim 3 including means for varying the load impedance for con- 4 trolling both audio frequency and radio frequency transmission, said variable load means comprising a variable condenser.

ELIMAR EBBIGHAUSEN. 

